## Volume of West Hill Pond

Since I have a bathymetric map of West Hill Pond, I thought it might be interesting to calculate the volume of the pond. The formula for calculating the volume of the frustum of a pyramid is $V = \frac{1}{3} h \left( A_1 + A_2 + \sqrt{A_1 A_2} \right)$ where $h$ is the height of the frustum, $A_1$ is the base area of the top of the frustum, and $A_2$ is the base area of the bottom of the frustum.1 This formula can be used with bathymetric contours to approximate the volume of a water body.2 Applying the formula to the bathymetric map of West Hill Pond results in a calculated volume of 9.3 × 106 m3, or 2.5 billion gallons.

Also available is the bathymetric contour shapefile used.

As I wrote last month, I recently got a set of NavSpark NS-RAW receivers. These can be used as a RTK GPS receiver system, but some sort of data link is needed. For shorter distances, XBee modules work well. Since I needed a convenient method for connecting the two devices together, both for the base station and the rover, I created an adapter board.

## NavSpark versus NS-RAW

Today I received the NavSpark and two NS-RAW GPS receivers I preordered from SkyTraq back in January. The NavSpark is a programmable SPARC-based GPS receiver, while the NS-RAW is one of the cheapest GPS receivers available with raw measurement output for RTK positioning. In recent months, it became clear that the two receivers would be virtually identical hardware-wise, just with different firmware.

On receiving the boards, the first thing I did was look for the differences. The most obvious difference is that the NavSpark has version 1.4 of the PCB, while the NS-RAW is built using version 1.3. The only difference I could find between the revisions is that version 1.3 left out the pull-up resistor on the SDA I2C line. SkyTraq seems to have used the flawed boards for the NS-RAW since it is not supposed to be programmable and thus won’t make use of I2C. This extra resistor can be seen below; version 1.3 is on the left, while version 1.4 is on the right.